System and method for engine poppet valve diagnostics

ABSTRACT

Systems and methods for determining operation of a cylinder deactivating/reactivating device are disclosed. In one example, a warm engine is rotated without being supplied fuel to determine the presence or absence of valve actuator degradation. Degraded valve actuators may be determined when there is a lack of a temperature rise in the engine exhaust system.

BACKGROUND AND SUMMARY

Intake poppet valves and exhaust poppet valves of an engine cylinder maybe selectively deactivated to conserve fuel. The intake and exhaustvalves may be selectively activated and deactivated viaelectromechanical actuators that may from time to time leave the valvesin a deactivated state. On the other hand, the electromechanicalactuators may allow the intake and exhaust valves to continue to operateeven though the intake and exhaust valves were commanded to adeactivated state. If the intake and exhaust valves continue to operatewhen the valve actuators are commanded to deactivate the valves, freshair may be pumped to the engine's exhaust system where it may affectcatalyst activity, thereby degrading vehicle emissions. Conversely, ifthe valves continue to be deactivated after the valve actuators arecommanded to activate the valves, the engine may produce less power thanis desired and fuel may accumulate in cylinders having valves thatremain deactivated.

One way to determine whether or not valve actuators are activating anddeactivating intake and exhaust poppet valves may be to measure cylinderpressure during a cycle of a cylinder. Alternatively, sensors may beplaced to sense the position of the valve actuators to determine if thevalve actuators reach their commanded position. However, cylinderpressure sensors and valve actuator position sensors may increase systemcost significantly. Therefore, it may be desirable to provide a way ofdetermining if intake and exhaust valve actuators are performing as isexpected without having to deploy cylinder pressure sensors or valveactuator position sensors.

The inventor herein has recognized the above mentioned issues and hasdeveloped an engine operating method, comprising: rotating an enginewithout combusting fuel via a controller; indicating valve actuatordegradation in response to lack of a temperature increase in an exhaustsystem after commanding activation of poppet valves of one or moreengine cylinders while rotating the engine without combusting fuel; andadjusting operation of the engine in response to the indication of valveactuator degradation.

By sampling a temperature of gases flowing through an exhaust system, itmay be possible to provide the technical result of determining whetheror not intake and exhaust valve actuators are operating as is expected.In one example, hot exhaust gases may be trapped in one or more enginecylinders after combustion in the engine has ceased. At the same time,intake and exhaust valves of other engine cylinders may operateaccording to a four stroke engine cycle. The engine may be rotated by anelectric machine, absent combustion within the engine, so that airflowing through the cylinders having operating intake and exhaust valvescools gases flowing through the exhaust system. After gas temperaturesin the exhaust system have cooled, the trapped hot exhaust gases incylinders having deactivated valves may then be released to the exhaustsystem by commanding formerly deactivated intake and exhaust valves toactive. If the temperature in the exhaust system increases, it may bejudged that the intake and exhaust valve actuators are operating as isexpected. However, if the temperature in the exhaust system does notincrease, it may be judged that the intake and exhaust valve operatorsare not operating as is expected because it may be inferred that exhaustgases remain trapped in the engine cylinder or that fresh air failed toenter cylinders and participate in combustion.

The present description may provide several advantages. In particular,the approach may provide improved diagnostics of engine cylinder valvedeactivation devices and intake and exhaust valves. Additionally, theapproach may provide cylinder diagnostics without increasing systemcost. Further, the approach may reduce engine emissions if degradedvalve operators are detected.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of one cylinder of an example enginesystem;

FIG. 2 shows an example cylinder valve activating/deactivating device;

FIGS. 3A-3B show example engine cylinder configurations for the engineof FIG. 1;

FIGS. 4 and 5 shows example cylinder valve deactivation mechanismdiagnostic sequences; and

FIGS. 6 and 7 show an example method for operating an engine.

DETAILED DESCRIPTION

The present description is related to diagnosing operation of an enginethat includes actuating mechanisms for cylinder poppet valves (e.g.,intake and exhaust valves). The actuating mechanisms may be included inthe engine to selectively deactivate and activate intake and exhaustvalves of engine cylinders, thereby enabling and disabling enginecylinder modes. An example actuating mechanism for cylinder valves isshown in FIG. 2. Two example engine cylinder configurations are shown inFIGS. 3A and 3B. Sequences for determining the presence or absence ofvalve and valve actuator degradation are shown in FIGS. 4 and 5. Themethod of FIGS. 6 and 7 may be applied to diagnose the presence orabsence of valve and valve actuator degradation.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. The controller 12receives signals from the various sensors in FIG. 1 and employs thevarious actuators of FIG. 1 to adjust engine operation based on receivedsignals and instructions stored in memory of the controller. Forexample, if controller 12 detects degradation of a cylinder poppet valveor poppet valve actuator, controller 12 may limit engine torqueproduction via limiting amounts of air and fuel that are delivered tothe engine.

Engine 10 is comprised of cylinder head 35 and block 33, which includecombustion chamber 30 and cylinder walls 32. Piston 36 is positionedtherein and reciprocates via a connection to crankshaft 40. Flywheel 97and ring gear 99 are coupled to crankshaft 40. Starter 96 (e.g., lowvoltage (operated with less than 30 volts) electric machine) includespinion shaft 98 and pinion gear 95. Pinion shaft 98 may selectivelyadvance pinion gear 95 to engage ring gear 99. Starter 96 may bedirectly mounted to the front of the engine or the rear of the engine.In some examples, starter 96 may selectively supply torque to crankshaft40 via a belt or chain. In one example, starter 96 is in a base statewhen not engaged to the engine crankshaft. In other examples, integratedstarter/generator (ISG) 111 may rotate engine 10 and ISG 111 may bedirectly coupled to crankshaft 40 or coupled to crankshaft 40 via abelt.

Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. The position of intake cam 51 may be determined byintake cam sensor 55. The position of exhaust cam 53 may be determinedby exhaust cam sensor 57. Intake valve 52 may be selectively activatedand deactivated by valve actuator device 59. Exhaust valve 54 may beselectively activated and deactivated by valve actuator device 58. Valveactuator devices 58 and 59 may be of the type shown in FIG. 2 or otherknown configurations.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Fuel injector 66 delivers liquid fuel in proportion to thepulse width from controller 12. Fuel is delivered to fuel injector 66 bya fuel system (not shown) including a fuel tank, fuel pump, and fuelrail (not shown). In one example, a high pressure, dual stage, fuelsystem may be used to generate higher fuel pressures.

In addition, intake manifold 44 is shown communicating with turbochargercompressor 162 and engine air intake 42. In other examples, compressor162 may be a supercharger compressor. Shaft 161 mechanically couplesturbocharger turbine 164 to turbocharger compressor 162. Optionalelectronic throttle 62 adjusts a position of throttle plate 64 tocontrol air flow from compressor 162 to intake manifold 44. Pressure inboost chamber 45 may be referred to a throttle inlet pressure since theinlet of throttle 62 is within boost chamber 45. The throttle outlet isin intake manifold 44. In some examples, throttle 62 and throttle plate64 may be positioned between intake valve 52 and intake manifold 44 suchthat throttle 62 is a port throttle. Wastegate 163 may be adjusted viacontroller 12 to allow exhaust gases to selectively bypass turbine 164to control the speed of compressor 162. Air filter 43 cleans airentering engine air intake 42. Throttle 62 is positioned downstream ofcompressor 162 in the direction of air flow into engine 10.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70 in exhaust system11. Alternatively, a two-state exhaust gas oxygen sensor may besubstituted for UEGO sensor 126. Engine exhaust system 11 includesexhaust manifold 48, temperature sensor 127, and converter 70. Converter70 can include multiple catalyst bricks, in one example. In anotherexample, multiple emission control devices, each with multiple bricks,can be applied. Converter 70 can be a three-way type catalyst in oneexample.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106 (e.g., non-transitory memory), random access memory 108, keepalive memory 110, and a conventional data bus. Controller 12 is shownreceiving various signals from sensors coupled to engine 10, in additionto those signals previously discussed, including: engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a position sensor 134 coupled to an accelerator pedal 130 forsensing force applied by human foot 132; a position sensor 154 coupledto brake pedal 150 for sensing force applied by human foot 132, ameasurement of engine manifold absolute pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof air mass entering the engine from sensor 120 (e.g., mass air flowsensor); and a measurement of throttle position from sensor 68.Barometric pressure may also be sensed (sensor not shown) for processingby controller 12. In a preferred aspect of the present description,engine position sensor 118 produces a predetermined number of equallyspaced pulses every revolution of the crankshaft from which engine speed(RPM) can be determined.

Controller 12 may also provide status information (e.g., indications ofdegradation or required maintenance) or receive input via human/machineinterface 175. Human/machine interface may be a touch screen panel,pushbutton interface, or other type of interface. During operation, eachcylinder within engine 10 typically undergoes a four stroke cycle: thecycle includes the intake stroke, compression stroke, expansion stroke,and exhaust stroke. During the intake stroke, generally, the exhaustvalve 54 closes and intake valve 52 opens. Air is introduced intocombustion chamber 30 via intake manifold 44, and piston 36 moves to thebottom of the cylinder so as to increase the volume within combustionchamber 30. The position at which piston 36 is near the bottom of thecylinder and at the end of its stroke (e.g. when combustion chamber 30is at its largest volume) is typically referred to by those of skill inthe art as bottom dead center (BDC).

During the compression stroke, intake valve 52 and exhaust valve 54 areclosed. Piston 36 moves toward the cylinder head so as to compress theair within combustion chamber 30. The point at which piston 36 is at theend of its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion.

During the expansion stroke, the expanding gases push piston 36 back toBDC. Crankshaft 40 converts piston movement into a rotational torque ofthe rotary shaft. Finally, during the exhaust stroke, the exhaust valve54 opens to release the combusted air-fuel mixture to exhaust manifold48 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

FIG. 2 shows an example cylinder valve actuator 58 for application inengine 10 shown in FIG. 1. Cylinder valve actuator 58 adjusts a liftand/or valve opening duration of a cylinder exhaust valve 54 in responseto engine operating conditions. Cylinder valve actuator 58 may providezero valve lift for one or more engine cycles to deactivate cylinderexhaust valves 54. Exhaust camshaft 53 is shown positioned above acylinder head 35 of an engine cylinder bank. Exhaust valve 54 isconfigured to open and close an exhaust port in a cylinder, such as thecylinder shown in FIG. 1. For example, exhaust valve 54 may beactuatable between an open position allowing gas exchange into or out ofa cylinder and a closed position substantially blocking gas exchangeinto or out of the cylinder. It should be understood that though onlyone valve is shown in FIG. 2; however, engine 10 shown in FIG. 1 mayinclude any number of cylinder valves. Further, a cylinder valveactuator similar to cylinder valve actuator 58 may be applied to engineintake valves. In addition, engine 10 of FIG. 1 may include any numberof cylinders with associated valves and a variety of different cylinderand valve configurations may be used, e.g., V-6, I-4, I-6, V-12, opposed4, and other engine types.

One or more cam towers or camshaft mounting regions may be coupled tocylinder head 35 to support exhaust camshaft 53. For example, cam tower216 is shown coupled to cylinder head 35 adjacent to exhaust valve 54.Though FIG. 2 shows a cam tower coupled to the cylinder head, in otherexamples, the cam towers may be coupled to other components of anengine, e.g., to a camshaft carrier or the cam cover. The cam towers maysupport overhead camshafts and may separate the lift mechanismspositioned on the camshafts above each cylinder.

Exhaust valve 54 may operate in a plurality of lift and duration modes,e.g., a high valve lift, low or partial valve lift, short openingduration, long opening duration, and zero valve lift. For example, asdescribed in more detail below, by adjusting cylinder cam mechanisms,the valves on one or more cylinders, e.g., exhaust valve 54, may beoperated in different lift modes based on engine operating conditions.

Exhaust camshaft 53 may include a plurality of cam lobes configured tocontrol the opening and closing of the exhaust valves. For example, FIG.2 shows a first cam lobe 212 and a second cam lobe 214 positioned abovevalve 54. The cams lobes may have different shapes and sizes to formlift profiles used to adjust an amount and timing of a lifting of valve54 while exhaust camshaft 53 rotates. For example, exhaust cam 212 maybe a full lift cam lobe and cam 214 may be a zero lift cam lobe. Though,FIG. 2 shows two lift profiles associated with first cam 212 and secondcam 214, it should be understood that any number of lift profile camsmay be present, e.g., three different cam lobes.

Exhaust camshaft 53 includes a mechanism 218 coupled to the camshaftabove the exhaust valve 54 for adjusting an amount of valve lift forthat exhaust valve 54 and/or for deactivating that exhaust valve bychanging a location of cam lobes along the camshaft relative to exhaustvalve 54. For example, the cam lobes 212 and 214 may be slideablyattached to the camshaft so that they can slide along the camshaft in anaxial direction on a per-cylinder basis. For example, a plurality of camlobes, e.g., cam lobes 212 and 214, positioned above each cylindervalve, e.g., exhaust valve 54, may be slid across the camshaft indirections indicated by arrow 245 to change a cam lobe profile coupledto the valve follower, e.g., follower 220 coupled to exhaust valve 54,to change the exhaust valve opening and closing durations and liftamounts. The valve cam follower 220 may include a roller finger follower(RFF) 222 which engages with a cam lobe positioned above valve 202. Forexample, in FIG. 2, roller 222 is shown engaging with full lift cam lobe212.

Additional follower elements not shown in FIG. 2 may further includepush rods, rocker arms, tappets, etc. Such devices and features maycontrol actuation of the intake valves and the exhaust valves byconverting rotational motion of the cams into translational motion ofthe valves. In other examples, the valves can be actuated via additionalcam lobe profiles on the camshafts, where the cam lobe profiles betweenthe different valves may provide varying cam lift height, cam duration,and/or cam timing. However, alternative camshaft (overhead and/orpushrod) arrangements could be used, if desired. Further, in someexamples, cylinders may each have only one exhaust valve and/or intakevalve, or more than one intake and/or exhaust valves. In still otherexamples, exhaust valves and intake valves may be actuated by a commoncamshaft. However, in an alternate example, at least one of the intakevalves and/or exhaust valves may be actuated by its own independentcamshaft or other device.

An outer sleeve 224 is splined to exhaust camshaft 53 and is coupled tothe cam lobes 212 and 214. Camshaft position relative to the enginecrankshaft is determined via rotation sensing camshaft position sensor295 and exhaust camshaft position indicator 290. Exhaust camshaft 53 maybe coupled to a cam phaser that is used to vary the valve timing withrespect to crankshaft position. By engaging a pin, e.g., one of the pins230 or 232, into a grooved hub in the outer sleeve, the axial positionof the sleeve can be repositioned so that a different cam lobe engagesthe cam follower coupled to exhaust valve 54 in order to change the liftof the exhaust valve 54. For example, sleeve 224 may include one or moredisplacing grooves, e.g., grooves 226 and 228, which extend around anouter circumference of the sleeve. The displacing grooves may have ahelical configuration around the outer sleeve and, in some examples, mayform a Y-shaped or V-shaped groove in the outer sleeve, where theY-shaped or V-shaped groove is configured to engage two differentactuator pins, e.g., first pin 230 and second pin 232, at differenttimes in order to move the outer sleeve to change a lift profile forexhaust valve 54. Sleeve 224 is shown in a first position while pin 232shifts sleeve 224 to the left side of FIG. 2. Sleeve 224 follows spline225 in an axial direction along exhaust camshaft 53 when profiles arebeing switched. Further, a depth of each groove in sleeve 224 maydecrease along a length of the groove so that after a pin is deployedinto the groove from a home position, the pin is returned to the homeposition by the decreasing depth of the groove as the sleeve andcamshaft rotate.

For example, as shown in FIG. 2, when first pin 230 is deployed intogroove 226, outer sleeve 224 will shift in a direction toward cam tower216 while exhaust camshaft 53 rotates, thereby positioning cam lobe 212above valve 202 and changing the valve lift profile. In order to switchback to cam lobe 214, second pin 232 may be deployed into groove 228which will shift outer sleeve 224 away from cam tower 216 to positioncam lobe 214 above valve 202. In some examples, multiple outer sleevescontaining lobes may be splined to exhaust camshaft 53. For example,outer sleeves may be coupled to cam lobes above every valve in engine 10or a select number of cam lobes above the valves.

Actuator pins 230 and 232 are included in a cam lobe switching actuator234 which adjusts the positions of the pins 230 and 232 in order toswitch cam lobes positioned above a valve 202. Exhaust cam lobeswitching actuator 234 includes an activating mechanism 236, which maybe hydraulically powered, or electrically actuated, or combinationsthereof. Activating mechanism 236 changes positions of the pins in orderto change lift profiles of a valve. For example, activating mechanism236 may be a coil coupled to both pins 230 and 232 so that when the coilis energized, e.g., via a current supplied thereto from the controlsystem, a force is applied to both pins to deploy both pins toward thesleeve.

Referring now to FIG. 3A, an example multi-cylinder engine that includestwo cylinder banks is shown. The engine includes cylinders andassociated components as shown in FIG. 1. Engine 10 includes eightcylinders each of which are labeled 310. Each of the eight cylinders isnumbered and the numbers of the cylinders are included within thecylinders. Fuel injectors 66 selectively supply fuel to each of thecylinders that are activated (e.g., combusting fuel during a cycle ofthe engine). Cylinders 1-8 may be selectively deactivated to improveengine fuel economy when less than the engine's full torque capacity isrequested. For example, cylinders 2, 3, 5, and 8 (e.g., a fixed patternof deactivated cylinders) may be deactivated during an engine cycle(e.g., two revolutions for a four stroke engine) and may be deactivatedfor a plurality of engine cycles while engine speed and load areconstant or very slightly. During a different engine cycle, a secondfixed pattern of cylinders 1, 4, 6, and 7 may be deactivated. Further,other patterns of cylinders may be selectively deactivated based onvehicle operating conditions. Additionally, engine cylinders may bedeactivated such that a fixed pattern of cylinders is not deactivatedover a plurality of engine cycles. Rather, cylinders that aredeactivated may change from one engine cycle to the next engine cycle.Each cylinder includes variable intake valve operators 51 and variableexhaust valve operators 53. An engine cylinder may be deactivated by itsvariable intake valve operators 51 and variable exhaust valve operatorsholding intake and exhaust valves of the cylinder closed during anentire cycle of the cylinder. Fuel flow to the cylinder ceases when acylinder is deactivated. An engine cylinder may be activated by itsvariable intake valve operators 51 and variable exhaust valve operators53 opening and closing intake and exhaust valves of the cylinder duringa cycle of the cylinder. Fuel is supplied to a cylinder that isactivated, but valves of a cylinder may open and close during a cylindercycle without supplying fuel to the cylinder during deceleration fuelshut-off. Engine 10 includes a first cylinder bank 304, which includesfour cylinders 1, 2, 3, and 4. Engine 10 also includes a second cylinderbank 302, which includes four cylinders 5, 6, 7, and 8. Cylinders ofeach bank may be active or deactivated during a cycle of the engine.

Engine 10 is also shown coupled to transmission 320. Transmission 320may be a fixed ratio transmission, dual clutch transmission, constantvelocity transmission, or other known type of transmission. Sensor 322may provide an indication of the position of shifter 321. For example,sensor 322 may indicate that transmission is engaged in park, neutral,reverse, or drive. The output of sensor 322 may be input to controller12 of FIG. 1.

Referring now to FIG. 3B, an example multi-cylinder engine that includesone cylinder bank is shown. The engine includes cylinders and associatedcomponents as shown in FIG. 1. Engine 10 includes four cylinders 310.Each of the four cylinders is numbered and the numbers of the cylindersare included within the cylinders. Fuel injectors 66 selectively supplyfuel to each of the cylinders that are activated (e.g., combusting fuelduring a cycle of the engine with intake and exhaust valves opening andclosing during a cycle of the cylinder that is active). Cylinders 1-4may be selectively deactivated (e.g., not combusting fuel during a cycleof the engine with intake and exhaust valves held closed over an entirecycle of the cylinder being deactivated) to improve engine fuel economywhen less than the engine's full torque capacity is requested. Forexample, cylinders 2 and 3 (e.g., a fixed pattern of deactivatedcylinders) may be deactivated during a plurality of engine cycles (e.g.,two revolutions for a four stroke engine). During a different enginecycle, a second fixed pattern cylinders 1 and 4 may be deactivated overa plurality of engine cycles. Further, other patterns of cylinders maybe selectively deactivated based on vehicle operating conditions.Additionally, engine cylinders may be deactivated such that a fixedpattern of cylinders is not deactivated over a plurality of enginecycles. Rather, cylinders that are deactivated may change from oneengine cycle to the next engine cycle. In this way, the deactivatedengine cylinders may rotate or change from one engine cycle to the nextengine cycle.

Engine 10 includes a single cylinder bank 350, which includes fourcylinders 1-4. Cylinders of the single bank may be active or deactivatedduring a cycle of the engine. Each cylinder includes variable intakevalve operators 51 and variable exhaust valve operators 53. An enginecylinder may be deactivated by its variable intake valve operators 51and variable exhaust valve operators holding intake and exhaust valvesof the cylinder closed during a cycle of the cylinder. Fuel flow isceased to a cylinder that is deactivated. An engine cylinder may beactivated by its variable intake valve operators 51 and variable exhaustvalve operators 53 opening and closing intake and exhaust valves of thecylinder during a cycle of the cylinder. Fuel is supplied to a cylinderthat is activated, but valves of a cylinder may open and close during acylinder cycle without supplying fuel to the cylinder duringdeceleration fuel shut-off.

Engine 10 is also shown coupled to transmission 360. Transmission 360may be a fixed ratio transmission, dual clutch transmission, constantvelocity transmission, or other known type of transmission. Sensor 362may provide an indication of the position of shifter 361. For example,sensor 362 may indicate that transmission is engaged in park, neutral,reverse, or drive. The output of sensor 362 may be input to controller12 of FIG. 1.

Thus, the system of FIGS. 1-3B provides for an engine system,comprising: an engine including one or more cylinder valve deactivatingmechanisms and an exhaust system; an electric machine; and a controllerincluding executable instructions stored in non-transitory memory toadjust operation of the engine in response to an indication ofdegradation of the one or more cylinder valve deactivating mechanisms,the indication of degradation based on a temperature in the exhaustsystem while the electric machine is rotating the engine and while fuelis not supplied to the engine. The indication of valve or valve actuatordegradation may be determined via an absence of a temperature increasein the engine's exhaust system. The engine system further comprisesproviding the indication of degradation of the one or more cylindervalve deactivation mechanisms when exhaust temperature does not increasewhile the electric machine is rotating the engine. The engine systemincludes where adjusting operation of the engine includes activating theone or more cylinder valve deactivating mechanisms. The engine systemincludes where adjusting operation of the engine includes ceasing tosupply fuel to one or more engine cylinders. The engine system furthercomprises additional instructions to selectively activate groups ofvalve deactivating mechanisms at different times. The engine systemfurther comprises additional instructions to open an engine throttlewhile rotating the engine.

Referring now to FIG. 4, a first example prophetic engine operatingsequence for a four cylinder (14), four stroke, engine is shown. Theoperating sequence of FIG. 4 may be produced via the system of FIGS.1-3B executing instructions of the method described in FIGS. 6 and 7.The plots of FIG. 4 are aligned in time and occur at the same time.Vertical markers at T0-T10 indicate times of particular interest duringthe sequence. The horizontal axis includes a break in time that isindicated between the two SSs located along the horizontal axis. Theduration of the break in time may be long or short.

The first plot from the top of FIG. 4 represents commanded valve modeversus time. The vertical axis represents commanded valve mode. Thehorizontal axis represents time and time increases from the left side ofthe plot to the right side of the plot. In this example, the engine iscapable of operating in only two valve modes at a point in time. Thevalve modes are indicated along the vertical axis and they include I2mode for operating the engine as a two cylinder engine (e.g., two enginecylinders with intake and exhaust valves opening and closing during anengine cycle while valves of two cylinders remain closed during theengine cycle) and I4 mode for operating the engine as a four cylinderengine (e.g., all four engine cylinders with intake and exhaust valvesopening and closing during an engine cycle). Trace 402 represents theengine valve mode state.

The second plot from the top of FIG. 4 represents an engine operatingstate versus time. The vertical axis represents engine operating stateand the engine is operating (e.g., combusting fuel) when trace 404 is ata higher level near the vertical axis arrow. The engine is not operating(e.g., not combusting fuel) when trace 404 is at a lower level near thehorizontal axis. The horizontal axis represents time and time increasesfrom the left hand side of the plot to the right hand side of the plot.Trace 404 represents engine state.

The third plot from the top of FIG. 4 represents temperature in theengine exhaust system (e.g., temperature of gases in the engine exhaustsystem) versus time. The vertical axis represents temperature in theengine exhaust system and the temperature increases in the direction ofthe vertical axis arrow. The horizontal axis represents time and timeincreases from the left hand side of the plot to the right hand side ofthe plot. Trace 406 represents temperature in the engine exhaust system.

The fourth plot from the top of FIG. 4 represents engine speed versustime. The vertical axis represents engine speed and engine speedincreases in the direction of the vertical axis arrow. The horizontalaxis represents time and time increases from the left hand side of theplot to the right hand side of the plot. Trace 408 represents enginespeed.

The fifth plot from the top of FIG. 4 represents engine throttleposition versus time. The vertical axis represents engine throttleposition and the opening amount of the engine throttle increases in thedirection of the vertical axis arrow. The horizontal axis representstime and time increases from the left hand side of the plot to the righthand side of the plot. Trace 410 represents throttle position.

The sixth plot from the top of FIG. 4 represents valve and/or valveactuator degradation state versus time. The vertical axis representsvalve and/or valve actuator degradation state and a valve and/or valveactuator is determined to be degraded when the valve degradation statetrace is at a higher level near the vertical axis arrow. A valve and/orvalve actuator is not determined to be degraded requested when the valvedegradation state trace is at a lower level near the horizontal axis.The horizontal axis represents time and time increases from the lefthand side of the plot to the right hand side of the plot. Trace 412represents the valve degradation state.

The seventh plot from the top of FIG. 4 represents valve diagnosticrequest state versus time. The vertical axis represents valve diagnosticrequest state and a valve and/or valve actuator is requested to bediagnosed when the valve diagnostic request state trace is at a higherlevel near the vertical axis arrow. A valve diagnostic is not requestedwhen the valve diagnostic request state trace is at a lower level nearthe horizontal axis. The horizontal axis represents time and timeincreases from the left hand side of the plot to the right hand side ofthe plot. Trace 414 represents the valve degradation state.

At time T0, the engine is operating in a four cylinder mode where allfour engine cylinders are combusting fuel during a cycle of the engine.The intake and exhaust valves of each cylinder are opened and closedduring an engine cycle. The exhaust system temperature is at a middlelevel indicating hot exhaust gases are in the engine cylinders and theexhaust system. The engine speed is at a middle level and the enginethrottle is partially open. The valve degradation state indicates thatvalve and/or valve actuator are not degraded and the valve diagnosticstate indicates that the valve diagnostic is not presently requested.

At time T1, the engine continues to operate in four cylinder mode, but avalve diagnostic is requested. The valve diagnostic may be requestedresponsive to vehicle operating conditions (e.g., distance traveled by avehicle, hours of engine operation, engine air-fuel ratio variation,etc.). The exhaust system temperature remains at an elevated temperatureand engine speed remains at a middle level. The throttle remains at amiddle position and valve degradation is not indicated.

Just before time T2, an engine stop request is provided by a human orautonomous driver is asserted (not shown) and the engine valves of twoengine cylinders are commanded deactivated to trap exhaust in the twoengine cylinders. In this example, the valves that are commandeddeactivated are transitioned to a deactivated state. The enginecontinues to operate and the exhaust system temperature remains at amiddle level. The engine speed also remains at a middle level. Thethrottle remains partially open and valve degradation is not indicated.

At time T2, the engine is stopped (not combusting fuel) and the enginespeed begins to decline. The engine includes two cylinders havingactivated intake and exhaust valves (e.g., intake and exhaust valvesthat open and close during an engine cycle) and two cylinders havingintake and exhaust valves that are deactivated (e.g., intake and exhaustvalves that are commanded held closed for an entire engine cycle). Theexhaust temperature remains at a middle level and the engine speed is ata middle level when combustion ceases. Valve degradation is notindicated and the valve diagnostic request remains asserted.

Between time T2 and time T3, the engine stops rotating and valves of twocylinders are in an activated mode (e.g., the intake and exhaust valveswill open and close during an engine cycle when the engine rotates) andvalves of two cylinders are in a deactivated mode (e.g., the intake andexhaust valve do not open during an engine cycle when the enginerotates). The exhaust system temperature decreases due to a small amountof air passing through the engine without participating in combustionwhile the engine decelerates to zero rotating speed, then the exhaustsystem temperature increases as air flow stops and the engine exhaustsystem heats gases in the exhaust system. The throttle is fully closedand valve degradation is not indicated. The valve diagnostic requestremains asserted to indicate that the valve diagnostic remains active.

At time T3, the engine is rotated via an electric machine (e.g., ISG 111shown in FIG. 1) while valves of two cylinders remain activated andvalves of two cylinders remain deactivated. Hot exhaust gas is trappedin the cylinders having deactivated intake and exhaust valves. Enginespeed begins to increase and the engine is not combusting fuel. Thethrottle is opened to increase the flow of fresh air through the exhaustsystem. Valve and/or valve actuator degradation is not indicated and thevalve diagnostic request remains asserted.

Between time T3 and time T4, fresh air is pumped into the exhaust systemvia the cylinders that have activated intake and exhaust valves. Hotexhaust gas remains trapped in engine cylinders with deactivated intakeand exhaust valves and work is performed on the exhaust gases in theengine cylinders with deactivated intake and exhaust valves. The exhaustsystem temperature decreases as fresh air is pumped through the exhaustsystem. The engine continues to be rotated via the electric machine andthe throttle remains open. Valve and/or valve actuator degradation isnot indicated and the valve diagnostic state remains asserted.

At time T4, the deactivated intake and exhaust valves of two cylindersare commanded activated so that exhaust gases trapped in the cylinderswith formerly deactivated intake and exhaust valves may be ejected intothe exhaust system. The intake and exhaust valves activate in responseto the command. The valve mode switches from 12 to 14 to indicateactivation of the intake and exhaust valves. The engine is rotated bythe electric machine and combustion is absent in engine cylinders.Engine speed continues at its previous level and the throttle remainsopen. Valve and/or valve actuator degradation is not indicated and thevalve diagnostic request remains asserted.

Between time T4 and time T5, the exhaust temperature increases as hotgases are released from the two cylinders that previously haddeactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously two deactivated cylinders are operating as is expected. Allengine intake and exhaust valves are activated and the engine is notcombusting. The engine continues to be rotated at its prior speed viathe electric machine and the throttle remains open. Valve and/or valveactuator degradation is not indicated and the valve diagnostic stateremains asserted.

At time T5, the valve diagnostic request is withdrawn and the electricmachine ceases to rotate the engine. The engine throttle is closed andvalve degradation is not indicated. The engine remains in I4 valve modeand the engine is not combusting fuel.

In this way, temperature of an exhaust system may confirm operation ofintake and exhaust valves. The engine need not be combusting air andfuel while the valve diagnostic is performed. Further, by not combustingfuel in the engine, exhaust gas temperature may be controlled toindicate the presence or absence of valve and/or valve actuatordegradation. Consequently, the person driving the vehicle does not haveto be disturbed to perform the valve diagnostic. The sequence continuesuntil the time break between time T5 and time T6.

At time T6, the engine is operating in four cylinder mode and a valvediagnostic is requested. The exhaust system temperature is at anelevated temperature and engine speed at a middle level. The throttle isat a middle position and valve degradation is not indicated.

Just before time T7, an engine stop request is provided by a human orautonomous driver is asserted (not shown) and the intake and exhaustvalves of two engine cylinders are commanded deactivated to trap exhaustin the two engine cylinders. However, in this example, the intake andexhaust valves that are commanded to deactivate do not deactivate. Theengine continues to operate and the exhaust system temperature remainsat a middle level. The engine speed also remains at a middle level. Thethrottle remains partially open and valve degradation is not indicated.

At time T7, the engine is stopped (not combusting fuel) and the enginespeed begins to decline. The engine may be stopped via ceasing to supplyfuel to the engine. The engine includes two cylinders having activatedintake and exhaust valves and two cylinders having intake and exhaustvalves that are commanded deactivated, but that are not actuallydeactivated. The exhaust temperature remains at a middle level and theengine speed is at a middle level when combustion ceases. Valve and/orvalve actuator degradation is not indicated and the valve diagnosticrequest remains asserted.

Between time T7 and time T8, the engine stops rotating and intake andexhaust valves of all cylinders are activated, but intake and exhaustvalves of two cylinders remain commanded deactivated. The exhaust systemtemperature decreases due to a small amount of air passing through theengine without participating in combustion as the engine decelerates tozero rotational speed, then the exhaust system temperature increases asair flow stops and the engine exhaust system heats gases in the exhaustsystem. The throttle is fully closed and valve and/or valve actuatordegradation is not indicated. The valve diagnostic request remainsasserted to indicate that the valve diagnostic remains active.

At time T8, the engine is rotated via an electric machine (e.g., ISG 111shown in FIG. 1) while intake and exhaust valves of all four cylindersremain activated and intake and exhaust valves of two cylinders arecommanded deactivated. Hot exhaust gas would be trapped in the cylindershaving deactivated intake and exhaust valves, but in this example, thecommanded deactivated intake and exhaust valves continue to operate.Engine speed begins to increase and the engine is not combusting fuel.The throttle is opened to increase the flow of fresh air through theexhaust system. Valve and/or valve actuator degradation is not indicatedand the valve diagnostic request remains asserted.

Between time T8 and time T9, fresh air is pumped into the exhaust systemvia all cylinders. Thus, air is pumped through cylinders that haveintake and exhaust valves commanded deactivated. The fresh air that ispumped through the engine decreases the temperature in the exhaustsystem. The engine continues to be rotated via the electric machine andthe throttle remains open. Valve and/or valve actuator degradation isnot indicated and the valve diagnostic state remains asserted.

At time T9, the intake and exhaust valves of the two cylinders that arecommanded deactivated are commanded activated to determine if thetemperature in the exhaust system increases in response to reactivatingthe valves that were commanded deactivated. The valve mode switches from12 to 14 to indicate all valves are commanded active. The engine isrotated by the electric machine and combustion is absent in enginecylinders. Engine speed continues at its previous level and the throttleremains open. Valve and/or valve actuator degradation is not indicatedand the valve diagnostic request remains asserted.

Between time T9 and time T10, the exhaust temperature continues todecline since exhaust gas is not ejected to the exhaust system fromcylinders that had intake and exhaust valves previously commandeddeactivated. The continued decrease in exhaust temperature indicatesthat the intake and exhaust valves of the previously two deactivatedcylinders did not operate as is expected. All engine intake and exhaustvalves are activated and the engine is not combusting fuel. The enginecontinues to be rotated at its prior speed via the electric machine andthe throttle remains open. Valve and/or valve actuator degradation isnow indicated because the exhaust system temperature failed to increaseafter reactivating the deactivated intake and exhaust valves. The valvediagnostic state remains asserted. Engine actuators may be adjusted inresponse to the indication of valve and/or valve actuator degradation asis described in further detail in the description of method 600.

At time T10, the valve diagnostic request is withdrawn and the electricmachine ceases to rotate the engine. The engine throttle is closed andvalve degradation is not indicated. The engine remains in I4 valve modeand the engine is not combusting fuel.

In this way, temperature of an exhaust system may confirm degradation ofintake and exhaust valves and their valve operators. The engine need notbe combusting air and fuel while the intake and exhaust valve diagnosticis performed. Consequently, the person driving the vehicle does not haveto be disturbed to perform the valve diagnostic.

Referring now to FIG. 5, an example prophetic engine operating sequencefor a four cylinder (14), four stroke, engine is shown. The operatingsequence of FIG. 5 may be produced via the system of FIGS. 1-3Bexecuting instructions of the method described in FIGS. 6 and 7. Theplots of FIG. 5 are aligned in time and occur at the same time. Verticalmarkers at T20-T35 indicate times of particular interest during thesequence. The horizontal axis includes a break in time that is indicatedbetween the two SSs located along the horizontal axis. The duration ofthe break in time may be long or short.

The first plot from the top of FIG. 5 represents commanded valve modeversus time. The vertical axis represents commanded valve mode. Thehorizontal axis represents time and time increases from the left side ofthe plot to the right side of the plot. In this example, the engine iscapable of operating in one of four valve modes at a point in time. Thevalve modes are indicated along the vertical axis and include I1 modefor operating the engine as a single cylinder engine (e.g., one enginecylinder with intake and exhaust valves opening and closing during anengine cycle while valves of three cylinders remain closed during theengine cycle), I2 mode for operating the engine as a two cylinder engine(e.g., two engine cylinders with intake and exhaust valves opening andclosing during an engine cycle while valves of two cylinders remainclosed during the engine cycle), I3 mode for operating the engine as athree cylinder engine (e.g., three engine cylinders with intake andexhaust valves opening and closing during an engine cycle while valvesof one cylinder remain closed during the engine cycle), and I4 mode foroperating the engine as a four cylinder engine with all intake andexhaust valves opening and closing during an engine cycle. Trace 502represents the engine valve mode state.

The second plot from the top of FIG. 5 represents an engine operatingstate versus time. The vertical axis represents engine operating stateand the engine is operating (e.g., combusting fuel) when trace 504 is ata higher level near the vertical axis arrow. The engine is not operating(e.g., not combusting fuel) when trace 504 is at a lower level near thehorizontal axis. The horizontal axis represents time and time increasesfrom the left hand side of the plot to the right hand side of the plot.Trace 504 represents engine state.

The third plot from the top of FIG. 5 represents temperature in theengine exhaust system (e.g., temperature of gases in the engine exhaustsystem) versus time. The vertical axis represents temperature in theengine exhaust system and the temperature increases in the direction ofthe vertical axis arrow. The horizontal axis represents time and timeincreases from the left hand side of the plot to the right hand side ofthe plot. Trace 506 represents temperature in the engine exhaust system.

The fourth plot from the top of FIG. 5 represents engine speed versustime. The vertical axis represents engine speed and engine speedincreases in the direction of the vertical axis arrow. The horizontalaxis represents time and time increases from the left hand side of theplot to the right hand side of the plot. Trace 508 represents enginespeed.

The fifth plot from the top of FIG. 5 represents engine throttleposition versus time. The vertical axis represents engine throttleposition and the opening amount of the engine throttle increases in thedirection of the vertical axis arrow. The horizontal axis representstime and time increases from the left hand side of the plot to the righthand side of the plot. Trace 510 represents throttle position.

The sixth plot from the top of FIG. 5 represents valve and/or valveactuator degradation state versus time. The vertical axis representsvalve and/or valve actuator degradation state and a valve and/or valveactuator is determined to be degraded when the valve degradation statetrace is at a higher level near the vertical axis arrow. A valve and/orvalve actuator is not determined to be degraded requested when the valvedegradation state trace is at a lower level near the horizontal axis.The horizontal axis represents time and time increases from the lefthand side of the plot to the right hand side of the plot. Trace 512represents the valve degradation state.

The seventh plot from the top of FIG. 5 represents valve diagnosticrequest state versus time. The vertical axis represents valve diagnosticrequest state and a valve and/or valve actuator is requested to bediagnosed when the valve diagnostic request state trace is at a higherlevel near the vertical axis arrow. A valve diagnostic is not requestedwhen the valve diagnostic request state trace is at a lower level nearthe horizontal axis. The horizontal axis represents time and timeincreases from the left hand side of the plot to the right hand side ofthe plot. Trace 514 represents the valve degradation state.

At time T20, the engine is operating in a four cylinder mode where allfour engine cylinders are combusting fuel during a cycle of the engine.The intake and exhaust valves of each cylinder are opened and closedduring an engine cycle. The exhaust system temperature is at a middlelevel indicating hot exhaust gases are in the engine cylinders and theexhaust system. The engine speed is at a middle level and the enginethrottle is partially open. The valve degradation state indicates thatvalve and/or valve actuator are not degraded and the valve diagnosticstate indicates that the valve diagnostic is not presently requested.

At time T21, the engine continues to operate in four cylinder mode, buta valve diagnostic is requested. The valve diagnostic may be requestedresponsive to vehicle operating conditions (e.g., distance traveled by avehicle, hours of engine operation, engine air-fuel ratio variation,etc.). The exhaust system temperature remains at an elevated temperatureand engine speed remains at a middle level. The throttle remains at amiddle position and valve degradation is not indicated.

Just before time T22, an engine stop request is provided by a human orautonomous driver is asserted (not shown) and the engine valves of threeengine cylinders are commanded deactivated to trap exhaust in the threeengine cylinders. In this example, the valves that are commandeddeactivated are transitioned to a deactivated state. The enginecontinues to operate and the exhaust system temperature remains at amiddle level. The engine speed also remains at a middle level. Thethrottle remains partially open and valve degradation is not indicated.

At time T22, the engine is stopped (not combusting fuel) and the enginespeed begins to decline. The engine includes one cylinder havingactivated intake and exhaust valves (e.g., intake and exhaust valvesthat open and close during an engine cycle) and three cylinders havingintake and exhaust valves that are deactivated (e.g., intake and exhaustvalves that are commanded held closed for an entire engine cycle). Theexhaust temperature remains at a middle level and the engine speed is ata middle level when combustion ceases. Valve degradation is notindicated and the valve diagnostic request remains asserted.

Between time T22 and time T23, the engine stops rotating and valves ofone cylinder are in an activated mode (e.g., the intake and exhaustvalves will open and close during an engine cycle when the enginerotates) and valves of three cylinders are in a deactivated mode (e.g.,the intake and exhaust valve do not open during an engine cycle when theengine rotates). The exhaust system temperature decreases due to a smallamount of air passing through the engine without participating incombustion as the engine decelerates to zero rotational speed, then theexhaust system temperature increases as air flow stops and the engineexhaust system heats gases in the exhaust system. The throttle is fullyclosed and valve degradation is not indicated. The valve diagnosticrequest remains asserted to indicate that the valve diagnostic remainsactive.

At time T23, the engine is rotated via an electric machine (e.g., ISG111 shown in FIG. 1) while valves of one cylinder remain activated andvalves of three cylinders remain deactivated. Hot exhaust gas is trappedin the cylinders having deactivated intake and exhaust valves. Enginespeed begins to increase and the engine is not combusting fuel. Thethrottle is opened to increase the flow of fresh air through the exhaustsystem. Valve degradation is not indicated and the valve diagnosticrequest remains asserted.

Between time T23 and time T24, fresh air is pumped into the exhaustsystem via the one cylinder having activated intake and exhaust valves.Hot exhaust gas remains trapped in engine cylinders with deactivatedintake and exhaust valves and work is performed on the exhaust gases inthe engine cylinders with deactivated intake and exhaust valves. Theexhaust system temperature decreases as fresh air is pumped through theexhaust system. The engine continues to be rotated via the electricmachine and the throttle remains open. Valve degradation is notindicated and the valve diagnostic state remains asserted.

At time T24, the deactivated intake and exhaust valves of two cylindersare commanded activated so that exhaust gases in the second cylinderwith formerly deactivated intake and exhaust valves may be ejected intothe exhaust system. The intake and exhaust valves activate in responseto the command. The valve mode switches from I1 to I2 to indicatecommanded activation of the intake and exhaust valves of two cylinders.The engine is rotated by the electric machine and combustion is absentin engine cylinders. Engine speed continues at its previous level andthe throttle remains open. Valve and/or valve actuator degradation isnot indicated and the valve diagnostic request remains asserted.

Between time T24 and time T25, the exhaust temperature increases a smallamount as hot gases are released from the one cylinder that previouslyhad deactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously deactivated cylinder (e.g., the second cylinder) areoperating as is expected. The engine is not combusting fuel and itcontinues to be rotated via the electric machine. The engine continuesto be rotated at its prior speed and the throttle remains open. Valveand/or valve actuator degradation is not indicated and the valvediagnostic state remains asserted.

At time T25, the deactivated intake and exhaust valves of threecylinders are commanded activated so that exhaust gases in the thirdcylinder with formerly deactivated intake and exhaust valves may beejected into the exhaust system. The intake and exhaust valves activatein response to the command. The valve mode switches from I2 to I3 toindicate commanded activation of the intake and exhaust valves of threecylinders. The engine is rotated by the electric machine and combustionis absent in engine cylinders. Engine speed continues at its previouslevel and the throttle remains open. Valve and/or valve actuatordegradation is not indicated and the valve diagnostic request remainsasserted.

Between time T25 and time T26, the exhaust temperature increases a smallamount as hot gases are released from the one cylinder that previouslyhad deactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously deactivated cylinder (e.g., the third cylinder) are operatingas is expected. The engine is not combusting fuel and it continues to berotated via the electric machine. The engine continues to be rotated atits prior speed and the throttle remains open. Valve and/or valveactuator degradation is not indicated and the valve diagnostic stateremains asserted.

At time T26, the intake and exhaust valves of all four cylinders arecommanded activated so that exhaust gases in the fourth cylinder withformerly deactivated intake and exhaust valves may be ejected into theexhaust system. The intake and exhaust valves activate in response tothe command. The valve mode switches from I3 to I4 to indicate commandedactivation of the intake and exhaust valves of all four cylinders. Theengine is rotated by the electric machine and combustion is absent inengine cylinders. Engine speed continues at its previous level and thethrottle remains open. Valve degradation is not indicated and the valvediagnostic request remains asserted.

Between time T26 and time T27, the exhaust temperature increases a smallamount as hot gases are released from the one cylinder that previouslyhad deactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously deactivated cylinder (e.g., the fourth cylinder) areoperating as is expected. The engine is not combusting fuel and itcontinues to be rotated via the electric machine. The engine continuesto be rotated at its prior speed and the throttle remains open. Valveand/or valve actuator degradation is not indicated and the valvediagnostic state remains asserted.

At time T27, the valve diagnostic request is withdrawn and the electricmachine ceases to rotate the engine. The engine throttle is closed andvalve degradation is not indicated. The engine remains in I4 valve modeand the engine is not combusting fuel.

In this way, temperature of an exhaust system may confirm operation ofintake and exhaust valves of individual cylinders. The engine need notbe combusting air and fuel while the valve diagnostic is performed.Consequently, a more through intake and exhaust valve diagnostic may beperformed. The sequence continues until the time break between time T27and time T28.

Before time T28, the engine is operating in a four cylinder mode whereall four engine cylinders are combusting fuel during a cycle of theengine. The intake and exhaust valves of each cylinder are opened andclosed during an engine cycle. The exhaust system temperature is at amiddle level indicating hot exhaust gases are in the engine cylindersand the exhaust system. The engine speed is at a middle level and theengine throttle is partially open. The valve degradation state indicatesthat valve and/or valve actuator are not degraded and the valvediagnostic state indicates that the valve diagnostic is not presentlyrequested.

At time T28, the engine continues to operate in four cylinder mode, buta valve diagnostic is requested. The exhaust system temperature remainsat an elevated temperature and engine speed remains at a middle level.The throttle remains at a middle position and valve degradation is notindicated.

Just before time T29, an engine stop request is provided by a human orautonomous driver is asserted (not shown) and the engine valves of threeengine cylinders are commanded deactivated to trap exhaust in the twoengine cylinders. In this example, the valves of the second cylinderthat are commanded to deactivate fail to transition to a deactivatedstate, but the valves of the remaining cylinders follow their respectivecommands. The engine continues to operate and the exhaust systemtemperature remains at a middle level. The engine speed also remains ata middle level. The throttle remains partially open and valvedegradation is not indicated.

At time T29, the engine is stopped (not combusting fuel) and the enginespeed begins to decline. The engine includes one cylinder havingactivated intake and exhaust valves (e.g., intake and exhaust valvesthat open and close during an engine cycle) and three cylinders havingintake and exhaust valves that are deactivated (e.g., intake and exhaustvalves that are commanded held closed for an entire engine cycle). Theexhaust temperature remains at a middle level and the engine speed is ata middle level when combustion ceases. Valve and/or valve actuatordegradation is not indicated and the valve diagnostic request remainsasserted.

Between time T29 and time T30, the engine stops rotating and valves ofone cylinder are in an activated mode (e.g., the intake and exhaustvalves will open and close during an engine cycle when the enginerotates) and valves of three cylinders are in a deactivated mode (e.g.,the intake and exhaust valve do not open during an engine cycle when theengine rotates). The exhaust system temperature decreases due to a smallamount of air passing through the engine without participating incombustion as the engine decelerates to zero rotational speed, then theexhaust system temperature increases as air flow stops and the engineexhaust system heats gases in the exhaust system. The throttle is fullyclosed and valve degradation is not indicated. The valve diagnosticrequest remains asserted to indicate that the valve diagnostic remainsactive.

At time T30, the engine is rotated via an electric machine (e.g., ISG111 shown in FIG. 1) while valves of one cylinder are commandedactivated and valves of three cylinders are commanded deactivated.However, valves of the first and second cylinder remain activated due todegradation of the valve actuator of the second cylinder. Hot exhaustgas is trapped in the cylinders having deactivated intake and exhaustvalves. Engine speed begins to increase and the engine is not combustingfuel. The throttle is opened to increase the flow of fresh air throughthe exhaust system. Valve and/or valve actuator degradation is notindicated and the valve diagnostic request remains asserted.

Between time T30 and time T31, fresh air is pumped into the exhaustsystem via two cylinders having activated intake and exhaust valves,despite valves of three cylinders being commanded deactivated. Hotexhaust gas remains trapped in engine cylinders with deactivated intakeand exhaust valves and work is performed on the exhaust gases in theengine cylinders with deactivated intake and exhaust valves. The exhaustsystem temperature decreases as fresh air is pumped through the exhaustsystem via two cylinders. The engine continues to be rotated via theelectric machine and the throttle remains open. Valve and/or valveactuator degradation is not indicated and the valve diagnostic stateremains asserted.

At time T31, the deactivated intake and exhaust valves of the secondcylinder are commanded activated along with the intake and exhaustvalves of the first cylinder so that it may be determined if hot exhaustwas trapped in the second cylinder with formerly deactivated intake andexhaust valves. The intake and exhaust valves activate in response tothe command. The valve mode switches from I1 to I2 to indicate commandedactivation of the intake and exhaust valves of two cylinders. The engineis rotated by the electric machine and combustion is absent in enginecylinders. Engine speed continues at its previous level and the throttleremains open. Valve degradation is not indicated and the valvediagnostic request remains asserted.

Between time T31 and time T32, the exhaust temperature decreases withoutincreasing since the intake and exhaust valves of the second cylinderdid not deactivate when they were commanded to deactivate. The decreasein exhaust temperature indicates that the intake and exhaust valves ofthe previously deactivated cylinder (e.g., the second cylinder) did notoperate as was expected. The engine is not combusting fuel and itcontinues to be rotated via the electric machine. The engine continuesto be rotated at its prior speed and the throttle remains open. Valvedegradation is not indicated and the valve diagnostic state remainsasserted.

At time T32, valve and/or valve actuator degradation is indicated.Because the intake and exhaust valves of the second cylinder werecommanded activated individually and the exhaust temperature did notincrease, the second cylinder may be specifically indicated as thecylinder with degraded intake and exhaust valves. Engine actuators maybe adjusted in response to the indication of valve and/or valve actuatordegradation as is described in further detail in the description ofmethod 600.

At time T33, the deactivated intake and exhaust valves of the thirdcylinder are commanded activated along with the intake and exhaustvalves of the first and second cylinders so that it may be determined ifhot exhaust was trapped in the third cylinder with formerly deactivatedintake and exhaust valves. The intake and exhaust valves are activatedin response to the command. The valve mode switches from I2 to I3 toindicate commanded activation of the intake and exhaust valves of threecylinders. The engine is rotated by the electric machine and combustionis absent in engine cylinders. Engine speed continues at its previouslevel and the throttle remains open. Valve and/or valve actuatordegradation is still indicated and the valve diagnostic request remainsasserted so that intake and exhaust valves of the remaining cylindersmay be diagnosed.

Between time T33 and time T34, the exhaust temperature increases a smallamount as hot gases are released from the one cylinder that previouslyhad deactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously deactivated cylinder (e.g., the third cylinder) are operatingas is expected. The engine is not combusting fuel and it continues to berotated via the electric machine. The engine continues to be rotated atits prior speed and the throttle remains open. Valve and/or valveactuator degradation is still indicated and the valve diagnostic stateremains asserted.

At time T34, the intake and exhaust valves of all four cylinders arecommanded activated so that exhaust gases in the fourth cylinder withformerly deactivated intake and exhaust valves may be ejected into theexhaust system. The intake and exhaust valves activate in response tothe command. The valve mode switches from I3 to I4 to indicate commandedactivation of the intake and exhaust valves of all four cylinders. Theengine is rotated by the electric machine and combustion is absent inengine cylinders. Engine speed continues at its previous level and thethrottle remains open. Valve and/or valve actuator degradation isindicated and the valve diagnostic request remains asserted.

Between time T34 and time T35, the exhaust temperature increases a smallamount as hot gases are released from the one cylinder that previouslyhad deactivated intake and exhaust valves. The increase in exhausttemperature indicates that the intake and exhaust valves of thepreviously deactivated cylinder (e.g., the fourth cylinder) areoperating as is expected. The engine is not combusting fuel and itcontinues to be rotated via the electric machine. The engine continuesto be rotated at its prior speed and the throttle remains open. Valvedegradation is still indicated and the valve diagnostic state remainsasserted.

At time T35, the valve diagnostic request is withdrawn and the electricmachine ceases to rotate the engine. The engine throttle is closed andvalve degradation is not indicated. The engine remains in I4 valve modeand the engine is not combusting fuel.

In this way, temperature of an exhaust system may confirm operation ofintake and exhaust valves of individual cylinders. The engine need notbe combusting air and fuel while the valve diagnostic is performed.Consequently, a more through intake and exhaust valve diagnostic may beperformed.

Referring now to FIGS. 6 and 7, a method for operating an engine anddetermining valve actuator degradation via engine exhaust temperature isdescribed. The method of FIGS. 6 and 7 may be incorporated into and maycooperate with the system of FIGS. 1-3B. Further, at least portions ofthe method of FIGS. 6 and 7 may be incorporated as executableinstructions stored in non-transitory memory while other portions of themethod may be performed via a controller transforming operating statesof devices and actuators in the physical world. Additionally, the enginemay be operating via combusting fuel and rotating according to a fourstroke cycle when method 600 is executed.

At 602, method 600 determines engine operating conditions. Engineoperating conditions may include but are not limited to engine operatingstate, engine speed, engine load, engine temperature, vehicle speed,engine exhaust system temperature, an actual total number of intake andexhaust valve profile switches since the vehicle was manufactured, anddistance driven by the vehicle. Method 600 proceeds to 604 after engineoperating conditions are determined.

At 604, method 600 judges whether or not cylinder valve actuatordiagnostics are desired. In one example, cylinder valve actuatordiagnostics may be desired after a vehicle travels a predetermineddistance, after cylinder valves have been deactivated more than athreshold amount of times, and if vehicle operating conditions aredesirable for cylinder valve actuator diagnostics. Cylinder valveactuator diagnostics may be desirable after vehicle passengers haveexited a vehicle, if a vehicle is being remotely started, or if thevehicle is a hybrid vehicle and driver demand is low enough to ceaseengine operation. If method 600 judges that cylinder valve actuatordiagnostics are desired, the answer is yes and method 600 proceeds to606. Otherwise, the answer is no and method 600 proceeds to 695.

At 695, method 600 operates the engine with intake and exhaust poppetvalves that are operable to open and close during an engine cycle.Method 600 may also operate the engine with poppet valves and actuatorsthat activate intake and exhaust valves according to commands. Forexample, if the engine is a V8 engine and it includes V6, V4, and V2cylinder modes, all modes may be available and entered subject to driverdemand torque and vehicle speed. However, if a valve actuator isdiagnosed as degraded such that a valve may not be activated anddeactivated as commanded, the engine may be prevented from entering V2and V4 cylinder modes. The particular cylinder mode that is activatedmay depend on driver demand torque and engine or vehicle speed. Further,if an intake or exhaust valve or valve actuator is determined to bedegraded, method 600 may limit the amount of torque the engine producesbased on the degraded valve or valve actuator. For example, method 600may prevent fuel flow to a cylinder that has an intake or exhaust valvethat does not open and close in response to commands. Further, method600 may prevent spark delivery to the same cylinder. The engine operatesvia combusting fuel according to a four stroke cycle. Method 600proceeds to exit.

At 606, method 600 judges if the engine includes valve actuators foractivating (e.g., activated intake and exhaust valves open and closeduring each engine cycle) and deactivating (e.g., deactivated intake andexhaust valves do not open and close during each engine cycle) eachvalve of each engine cylinder. Method 600 may judge if the engineincludes valve actuators for activating and deactivating each poppetvalve of each engine cylinder according to a value of a variable thatindicates the engine's configuration. If the value of the variableindicates that the engine includes valve actuators for activating anddeactivating each poppet valve of each cylinder, then the answer is yesand method 600 proceeds to 608. Otherwise, the answer is no and method600 proceeds to 650.

At 608, method 600 judges if an engine stop is requested and if thetransmission is engaged in park. In one example, an engine stop may berequested via a human driver providing input to a key switch,pushbutton, or other device that has a sole purpose of requesting anengine stop or start. Alternatively, an autonomous driver may request anengine stop via adjusting a value of a variable in controller memory.Similarly, method 600 may judge if the vehicle's transmission is engagedin park via determining a position of a shifter via a sensor. If method600 judges that an engine stop is requested and the vehicle'stransmission is engaged in park, the answer is yes and method 600proceeds to 610. Otherwise, the answer is no and method 600 proceeds to695.

At 610, method 600 deactivates intake and exhaust valves of selectedengine cylinders, stops combustion in the engine, and closes theengine's throttle. In one example as shown in FIG. 5, all intake andexhaust valves of all engine cylinders with the exception of intake andexhaust valves of one engine cylinder may be deactivated such that theintake and exhaust valves remain closed an entire time the enginerotates through an engine cycle (e.g., two revolutions). In otherexamples, intake and exhaust valves of predetermined engine cylindersmay be deactivated. The intake and exhaust valves of the cylinders aredeactivated such that each cylinder retains and does not exhaustcombusted gases. Method 600 proceeds to 612.

At 612, method 600 judges if combustion in the engine is stopped.Combustion may be allowed to continue until each cylinder that includesintake and exhaust valves that are deactivated holds combusted exhaustproducts. For example, if cylinder number one is on an intake strokewhen the engine stop is requested, then the engine continues combustionuntil the air inducted into cylinder number one participates incombustion with fuel injected into cylinder number one. The combustionbyproducts then remain trapped in cylinder number one by not opening theexhaust valves of cylinder number one after combustion occurs in thecompression stroke of cylinder number one. Similarly, combustion maycontinue in other engine cylinders until each engine cylinder that iscommanded to have deactivated intake and exhaust valves is trappingcombustion byproducts (e.g., exhaust gases). If method 600 judges thatcombustion in the engine has stopped, the answer is yes and method 600proceeds to 614. Otherwise, the answer is no and method 600 returns to612.

At 614, method 600 rotates the engine via an electric machine (e.g., ISG111 or starter 96 of FIG. 1). By rotating the engine, gases in theexhaust system may be cooled so that hot exhaust gases exiting cylindershaving formerly deactivated intake and exhaust valves may bedistinguished from cool air that passes through cylinders with activatedintake and exhaust valves. The engine exhaust system is cooled byflowing air through cylinders with activated valves while the enginerotates. Method 600 proceeds to 616.

At 616, method 600 determines engine exhaust system temperature. In oneexample, method 600 may determine a temperature of exhaust gases in theengine exhaust system via a temperature sensor. Output of thetemperature sensor is provided to the controller to determine engineexhaust system temperature. Method 600 proceeds to 618.

At 618, method 600 judges if a temperature of the exhaust system hasincreased after intake and exhaust valves of a cylinder that weredeactivated are reactivated. Method 600 may judge that temperature ofthe exhaust system has is increased if output of a temperature sensorindicates a higher exhaust temperature immediately after (within twoengine cycles) intake and exhaust valves of a cylinder are reactivatedas compared to exhaust temperature immediately before the intake andexhaust valves are activated. If method 600 judges that a higher exhausttemperature is observed, the answer is yes and method 600 proceeds to620. If method 600 judges that a higher exhaust temperature is notobserved, then method 600 proceeds to 620 if method 600 enters step 618without having reactivated intake and exhaust valves after deactivatingintake and exhaust valves of selected cylinders at 610. If method 600judges that a higher exhaust temperature is not observed and that method600 has reactivated intake and exhaust valves after deactivating intakeand exhaust valves of selected cylinders at 610, then the answer is noand method 600 proceeds to 630.

At 630, method 600 indicates valve degradation is present for thecylinder that has most recently had its intake and exhaust valvesreactivated. The indication may be made via changing a value of avariable in memory. Further, method 600 may provide a visual or audibleindication in a passenger compartment of the vehicle via a human/machineinterface. Method 600 proceeds to 632.

At 632, method 600 adjusts engine actuators in response to valve andvalve actuator degradation. In one example, where intake and/or exhaustvalves and/or valve actuators of a cylinder are determined to bedegraded, method 600 ceases to supply fuel to the cylinder havingdegraded valves and/or valve actuators. In another example, method 600may prevent other engine cylinders from being deactivated based onintake and/or exhaust valves and/or valve actuators so that the engineis able to operate in only a fraction of a total number of availablecylinder modes. For example, a V8 engine may be allowed to operate inonly V8 and V6 modes and may be prevented from entering V4 cylindermode. Further, method 600 may adjust the engine throttle responsive to afirst engine airflow and MAP relationship when intake and exhaust valveor valve actuator degradation is not present, and method 600 may adjustthe engine throttle responsive to a second engine airflow and MAPrelationship when intake and exhaust valve or valve actuator degradationis present. The engine actuators may be adjusted responsive to valveactuator degradation when the engine is restarted and combusting fuel.Method 600 proceeds to 620 after adjusting engine actuators.

At 620, method 600 judges if the engine has been rotating for athreshold amount of time since a most recent time when intake andexhaust valves of a cylinder were commanded activated. For example,intake and exhaust valves of cylinder number four may be commandedactivated at time t1, if method 600 judges that a threshold amount oftime has passed since time t1, then the answer is yes and method 600proceeds to 622. If method 600 judges that the engine has been rotatingfor a threshold amount of time since a most recent time when intake andexhaust valves of a cylinder were commanded activated, the answer is yesand method 600 proceeds to 622. Otherwise, the answer is no and method600 returns to 616.

At 622, method 600 judges if all intake and exhaust valves of all enginecylinders have been activated after select intake and exhaust valveswere deactivated at 610. In one example, activation and/or deactivationof intake and exhaust valves of a cylinder may be indicated by a valueof variables stored in controller memory. If the values of the variablesindicate that all intake and exhaust valves of all engine cylinders ofthe engine have been commanded activated, the answer is yes and method600 proceeds to 626. Otherwise, the answer is no and method 600 proceedsto 625.

At 626, method 600 ceases engine rotation via the electric machine andcloses the throttle. Method 600 exits after ceasing engine rotation andclosing the engine throttle.

At 625, method 600 activates intake and exhaust valves of a nextcylinder that had its valves deactivated at 610. For example, if a fourcylinder engine had intake and exhaust valves deactivated for cylinders2, 3, and 4 at 610 and intake and exhaust valves of cylinder number 2have already been activated, then method 600 may activate the intake andexhaust valves of cylinder number 3. Method 600 returns to 616.

In this way, method 600 may selectively deactivate and activate intakeand exhaust valves of individual cylinders where individual control overintake and exhaust valves is provided. If a temperature increase in theexhaust system is detected when the deactivated intake and exhaustvalves are reactivated, it may be determined that the intake and exhaustvalves and their actuators are operating as is expected. If atemperature increase is not detected in the engine exhaust system whenthe deactivated intake and exhaust valves are reactivated, it may bedetermined that the intake and exhaust valves and their actuators arenot operating as is expected.

At 650, method 600 judges if an engine stop is requested and if thetransmission is engaged in park. In one example, an engine stop may berequested via a human driver providing input to a key switch,pushbutton, or other device that has a sole purpose of requesting anengine stop or start. Alternatively, an autonomous driver may request anengine stop via adjusting a value of a variable in controller memory.Similarly, method 600 may judge if the vehicle's transmission is engagedin park via determining a position of a shifter via a sensor. If method600 judges that an engine stop is requested and the vehicle'stransmission is engaged in park, the answer is yes and method 600proceeds to 652. Otherwise, the answer is no and method 600 proceeds to696.

At 696, method 600 operates the engine with intake and exhaust poppetvalves that are operable to open and close during an engine cycle.Method 600 may also operate the engine with poppet valves and actuatorsthat activate intake and exhaust valves according to commands. Forexample, if the engine is a V8 engine and it includes V6, V4, and V2cylinder modes, all modes may be available and entered subject to driverdemand torque and vehicle speed. However, if a valve actuator isdiagnosed as degraded such that a valve may not be activated anddeactivated as commanded, the engine may be prevented from entering V2and V4 cylinder modes. The particular cylinder mode that is activatedmay depend on driver demand torque and engine or vehicle speed. Further,if an intake or exhaust valve or valve actuator is determined to bedegraded, method 600 may limit the amount of torque the engine producesbased on the degraded valve or valve actuator. For example, method 600may prevent fuel flow to a cylinder that has an intake or exhaust valvethat does not open and close in response to commands. Further, method600 may prevent spark delivery to the same cylinder. The engine operatesvia combusting fuel according to a four stroke cycle. Method 600proceeds to exit.

At 652, method 600 deactivates intake and exhaust valves of selectedengine cylinders, stops combustion in the engine, and closes theengine's throttle. In one example as shown in FIG. 4, all intake andexhaust valves of a fraction of engine cylinders may be deactivated suchthat the intake and exhaust valves remain closed an entire time theengine rotates through an engine cycle (e.g., two revolutions). Forexample, intake and exhaust valves of cylinders number 1 and 3 of a fourcylinder engine may be deactivated. In one example, the engine may notbe able to deactivate intake and exhaust valves of individual cylinders.Rather, it may only be allowed to deactivate a group of cylinders.Method 600 deactivates intake and exhaust valves of engine cylinders andproceeds to 654.

At 654, method 600 judges if combustion in the engine is stopped.Combustion may be allowed to continue until each cylinder that includesintake and exhaust valves that are deactivated holds combusted exhaustproducts. For example, if cylinder number one is on an intake strokewhen the engine stop is requested, then the engine continues combustionuntil the air inducted into cylinder number one participates incombustion with fuel injected into cylinder number one. The combustionbyproducts then remain trapped in cylinder number one by not opening theexhaust valves of cylinder number one after combustion occurs in thecompression stroke of cylinder number one. Similarly, combustion maycontinue in other engine cylinders until each engine cylinder that iscommanded to have deactivated intake and exhaust valves is trappingcombustion byproducts (e.g., exhaust gases). If method 600 judges thatcombustion in the engine has stopped, the answer is yes and method 600proceeds to 656. Otherwise, the answer is no and method 600 returns to654.

At 656, method 600 rotates the engine via an electric machine (e.g., ISG111 or starter 96 of FIG. 1). By rotating the engine, gases in theexhaust system may be cooled so that hot exhaust gases exiting cylindershaving formerly deactivated intake and exhaust valves may bedistinguished from cool air that passes through cylinders with activatedintake and exhaust valves. Method 600 proceeds to 658.

At 658, method 600 determines engine exhaust system temperature. In oneexample, method 600 may determine a temperature of exhaust gases in theengine exhaust system via a temperature sensor. Output of thetemperature sensor is provided to the controller to determine engineexhaust system temperature. Method 600 proceeds to 660.

At 660, method 600 judges if a temperature of the exhaust system hasincreased after intake and exhaust valves of a cylinder that weredeactivated are reactivated. Method 600 may judge that temperature ofthe exhaust system has is increased if output of a temperature sensorindicates a higher exhaust temperature immediately after (within twoengine cycles) intake and exhaust valves of one or more cylinders arereactivated as compared to exhaust temperature immediately before theintake and exhaust valves are activated. If method 600 judges that ahigher exhaust temperature is observed, the answer is yes and method 600proceeds to 662. If method 600 judges that a higher exhaust temperatureis not observed, then method 600 proceeds to 662 if method 600 entersstep 660 without having reactivated intake and exhaust valves afterdeactivating intake and exhaust valves of selected cylinders at 652. Ifmethod 600 judges that a higher exhaust temperature is not observed andthat method 600 has commanded reactivated intake and exhaust valvesafter deactivating intake and exhaust valves of selected cylinders at652, then the answer is no and method 600 proceeds to 670.

At 670, method 600 indicates valve degradation is present for thecylinder or cylinders that have most recently had their intake andexhaust valves reactivated. The indication may be made via changing avalue of a variable in memory. Further, method 600 may provide a visualor audible indication in a passenger compartment of the vehicle via ahuman/machine interface. Method 600 proceeds to 672.

At 672, method 600 adjusts engine actuators in response to valve and/orvalve actuator degradation. In one example, where intake and/or exhaustvalves and/or valve actuators of a cylinder are determined to bedegraded, method 600 ceases to supply fuel to the cylinder havingdegraded valves and/or valve actuators. In another example, method 600may prevent other engine cylinders from being deactivated based onintake and/or exhaust valves and/or valve actuators so that the engineis able to operate in only a fraction of a total number of availablecylinder modes. For example, a V8 engine may be allowed to operate inonly V8 and V6 modes and may be prevented from entering V4 cylindermode. Further, method 600 may adjust the engine throttle responsive to afirst engine airflow and MAP relationship when intake and exhaust valveor valve actuator degradation is not present, and method 600 may adjustthe engine throttle responsive to a second engine airflow and MAPrelationship when intake and exhaust valve or valve actuator degradationis present. The engine actuators may be adjusted responsive to valveactuator degradation when the engine is restarted and combusting fuel.Method 600 proceeds to 662 after adjusting engine actuators.

At 662, method 600 judges if the engine has been rotating for athreshold amount of time since a most recent time when intake andexhaust valves of a cylinder were commanded activated. For example,intake and exhaust valves of cylinder numbers one and four of a fourcylinder engine may be commanded activated at time t1, if method 600judges that a threshold amount of time has passed since time t1, thenthe answer is yes and method 600 proceeds to 664. If method 600 judgesthat the engine has been rotating for a threshold amount of time since amost recent time when intake and exhaust valves of one or more cylinderswere commanded activated, the answer is yes and method 600 proceeds to664. Otherwise, the answer is no and method 600 returns to 658.

At 664, method 600 judges if all intake and exhaust valves of all enginecylinders have been activated after select intake and exhaust valveswere deactivated at 652. In one example, activation and/or deactivationof intake and exhaust valves of a cylinder may be indicated by a valueof variables stored in controller memory. If the values of the variablesindicate that all intake and exhaust valves of all engine cylinders ofthe engine have been commanded activated, the answer is yes and method600 proceeds to 666. Otherwise, the answer is no and method 600 proceedsto 665.

At 666, method 600 ceases engine rotation via the electric machine andcloses the throttle. Method 600 exits after ceasing engine rotation andclosing the engine throttle.

At 665, method 600 activates intake and exhaust valves of a nextcylinder that had its valves deactivated at 652. For example, if a fourcylinder engine had intake and exhaust valves deactivated for cylinders2 and 3 at 652 and intake and exhaust valves of cylinders numbered 2 and3 have not already been activated, then method 600 may activate theintake and exhaust valves of cylinders numbered 2 and 3. Method 600returns to 658.

In this way, method 600 may selectively deactivate and activate intakeand exhaust valves of cylinders included in a group of cylinders whereindividual control over intake and exhaust valves is not provided. If atemperature increase is detected when the deactivated intake and exhaustvalves are reactivated, it may be determined that the intake and exhaustvalves and their actuators are operating as is expected. If atemperature increase is not detected when the deactivated intake andexhaust valves are reactivated, it may be determined that the intake andexhaust valves and their actuators are not operating as is expected.

Thus, method 600 provides for an engine operating method, comprising:rotating an engine without combusting fuel via a controller; indicatingvalve actuator degradation in response to lack of a temperature increasein an exhaust system after commanding activation of poppet valves of oneor more engine cylinders while rotating the engine without combustingfuel; and adjusting operation of the engine in response to theindication of valve actuator degradation. The method further comprisesdetermining the lack of temperature increase via output of a temperaturesensor. The method further comprising detecting a lack of temperatureincrease in the exhaust system. The method includes where adjustingengine operation includes activating all cylinders of the engine. Themethod includes where adjusting engine operation includes ceasing tosupply fuel to one or more engine cylinders.

In some examples, the method further comprises rotating the engine withintake and exhaust valves of one or more cylinders operating whilerotating the engine without combusting fuel before commanding activationof the poppet valves. The method includes where the poppet valvesinclude intake valves and exhaust valves. The method includes where theengine is rotated via an integrated starter/generator. The methodfurther comprises indicating absence of valve actuator degradation inresponse to a temperature increase in the exhaust system. The methodfurther comprises deactivating poppet valves of the one or more enginecylinders before or during rotating the engine without combusting fuel.

Method 600 also provides for an engine operating method, comprising:requesting to diagnose one or more intake and exhaust valves;deactivating intake and exhaust poppet valves of a first cylinder duringan engine stop in response to a request to diagnose one or more intakeand exhaust valves; rotating an engine without combusting fuel via acontroller; indicating valve actuator degradation in response to anabsence of an increase of a temperature in an exhaust system afteractivating the intake and exhaust poppet valves of the first cylinderwhile rotating the engine without combusting fuel; and adjustingoperation of the engine in response to the indication of valve actuatordegradation. The method includes detecting an absence of an increase intemperature in the exhaust system after activating intake and exhaustvalves. The method includes where deactivating intake and exhaust poppetvalves includes holding the intake and exhaust poppet valves closed foran entire engine cycle. The method further comprises indicating lack ofvalve actuator degradation in response to a presence of the increase ofthe temperature in the exhaust system after activating the intake andexhaust poppet valves. The method further comprises deactivating intakeand exhaust poppet valves of a second cylinder during the engine stop.The method further comprises indicating valve actuator degradation inresponse to an absence of an increase of a temperature in an exhaustsystem after activating the intake and exhaust poppet valves of thesecond cylinder while rotating the engine without combusting fuel, theintake and exhaust poppet valves of the second cylinder activated apredetermined amount of time after activating the intake and exhaustpoppet valves of the first cylinder. The method includes detecting anabsence of an increase of a temperature in the exhaust system afteractivating intake and exhaust valves of a second cylinder.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific examples are notto be considered in a limiting sense, because numerous variations arepossible. For example, the above technology can be applied to V-6, I-4,I-6, V-12, opposed 4, and other engine types. The subject matter of thepresent disclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. An engine operating method, comprising:rotating an engine without combusting fuel via a controller; indicatingvalve actuator degradation in response to lack of a temperature increasein an exhaust system after commanding activation of poppet valves of oneor more engine cylinders while rotating the engine without combustingfuel; and adjusting operation of the engine in response to theindication of valve actuator degradation.
 2. The method of claim 1,further comprising determining the lack of temperature increase viaoutput of a temperature sensor.
 3. The method of claim 1, whereadjusting engine operation includes activating all cylinders of theengine.
 4. The method of claim 1, where adjusting engine operationincludes ceasing to supply fuel to one or more engine cylinders.
 5. Themethod of claim 1, further comprising rotating the engine with intakeand exhaust valves of one or more cylinders operating while rotating theengine without combusting fuel before commanding activation of thepoppet valves.
 6. The method of claim 1, where the poppet valves includeintake valves and exhaust valves.
 7. The method of claim 1, where theengine is rotated via an integrated starter/generator.
 8. The method ofclaim 1, further comprising indicating absence of valve actuatordegradation in response to a temperature increase in the exhaust system.9. The method of claim 8, further comprising deactivating poppet valvesof the one or more engine cylinders before or during rotating the enginewithout combusting fuel.
 10. An engine operating method, comprising:deactivating intake and exhaust poppet valves of a first cylinder duringan engine stop in response to a request to diagnose one or more intakeand exhaust valves; rotating an engine without combusting fuel via acontroller; indicating valve actuator degradation in response to anabsence of an increase of a temperature in an exhaust system afteractivating the intake and exhaust poppet valves of the first cylinderwhile rotating the engine without combusting fuel; and adjustingoperation of the engine in response to the indication of valve actuatordegradation.
 11. The method of claim 10, where deactivating intake andexhaust poppet valves includes holding the intake and exhaust poppetvalves closed for an entire engine cycle.
 12. The method of claim 10,further comprising indicating lack of valve actuator degradation inresponse to a presence of the increase of the temperature in the exhaustsystem after activating the intake and exhaust poppet valves.
 13. Themethod of claim 10, further comprising deactivating intake and exhaustpoppet valves of a second cylinder during the engine stop.
 14. Themethod of claim 13, further comprising indicating valve actuatordegradation in response to an absence of an increase of a temperature inan exhaust system after activating the intake and exhaust poppet valvesof the second cylinder while rotating the engine without combustingfuel, the intake and exhaust poppet valves of the second cylinderactivated a predetermined amount of time after activating the intake andexhaust poppet valves of the first cylinder.
 15. An engine system,comprising: an engine including one or more cylinder valve deactivatingmechanisms and an exhaust system; an electric machine; and a controllerincluding executable instructions stored in non-transitory memory toadjust operation of the engine in response to an indication ofdegradation of the one or more cylinder valve deactivating mechanisms,the indication of degradation based on a temperature in the exhaustsystem while the electric machine is rotating the engine and while fuelis not supplied to the engine.
 16. The engine system of claim 15,further comprising providing the indication of degradation of the one ormore cylinder valve deactivation mechanisms when exhaust temperaturedoes not increase while the electric machine is rotating the engine. 17.The engine system of claim 15, where adjusting operation of the engineincludes activating the one or more cylinder valve deactivatingmechanisms.
 18. The engine system of claim 15, where adjusting operationof the engine includes ceasing to supply fuel to one or more enginecylinders.
 19. The engine system of claim 15, further comprisingadditional instructions to selectively activate groups of valvedeactivating mechanisms at different times.
 20. The engine system ofclaim 15, further comprising additional instructions to open an enginethrottle while rotating the engine.